The present invention relates to a trencher that can dig a curved trench.
Trenchers that use digging chains have long been known in the prior art. Generally, a trencher includes a carriage and a trencher boom that carries a digging chain having a series of digging blades. Typically, the digging chain is carried by a motor driven sprocket wheel and an idler pulley wheel which are mounted to a frame that can be moved into a digging position. Generally, the frame that carries the digging chain pivots at its base to tilt into contact with a working surface of soil or clay so that the digging chain can excavate a trench as the trencher moves across the working surface.
U.S. Pat. No. 4,483,084 by Caldwell et al. is exemplary of the prior art. Caldwell""s trencher includes a boom that pivots relative to a carriage so that it can dig at various angles and depths. If a shallow trench is desired, an operator of Caldwell""s trencher would pivot the trencher boom by a shallow angle. If a deep trench is desired, an operator would pivot the trencher boom of the Caldwell trencher until it reaches a steep angle.
The disadvantages of prior art trenchers arise when an operator wishes to dig a curved trench. For example, relatively shallow, circular trenches are needed for receiving the concrete footing of the foundation of a circular structure such as a grain bin or a tank. Trenches of greater depth that are excavated for water or electric power lines must often be dug around obstacles. Because the digging chains of prior art trenchers must generally pivot into a digging position, the digging chain of a prior art trencher contacts a work surface at a shallow angle when it is digging a shallow trench and often penetrates a work surface at a moderate angle when digging a deeper trench. If the trench is to be circular or curved, it becomes very difficult if not impossible to guide a shallow angled digging chain around a curved path while it is digging. A digging chain penetrating a working surface at a shallow or moderate angle will interfere with the walls of the trench if a curved section of trench is attempted. Moreover, in a prior art trencher, the digging chain is cantilevered away from the trencher carriage so that the center of the digging chain will swing through an arc as the carriage turns. Because it is not practical to turn a prior art trencher along a tightly curved path while it is digging a trench, intersecting trench sections must be dug to make a trench around an obstacle. Generally, significant amounts of material will accumulate where sections of the trench intersect. Material that accumulates at these intersections must be removed by hand digging. What is needed is a trencher that can easily dig circular or curved trenches and which can also smoothly transition from digging a straight trench to digging a curved trench when an obstacle is encountered.
Accordingly, it is an object of the present invention is to provide a trencher that can dig a curved trench. It is another object of the present invention to provide a trencher that can smoothly transition between excavating a straight section of trench and a curved section of trench. It is yet another object of the present invention to provide a trencher that has attachments for moving excavated material away from a trench as the trench is being excavated. It is still yet another object of the present invention to provide a trencher having adjustable earth moving blades that can be positioned for returning excavated material to a trench, for directing excavated material away from a trench or for scraping or smoothing a working surface.
These and other objects of the present invention are attained in an improved trencher which includes a carriage, a digging chain, a digging chain support frame and an upright boom structure. The carriage includes wheels for rolling across a working surface and a steering mechanism for turning the carriage. The digging chain support frame carries the digging chain and is mounted to the upright boom structure for upward and downward movement relative to the upright boom structure. The digging chain is carried by a pair of wheels that are rotatably mounted to the digging chain support frame and that are disposed so that the digging motion of the chain describes an upright path. The wheels include a sprocket wheel at the upper end of the digging chain support frame and an idler pulley wheel at the lower end of the digging chain support frame. A chain drive motor powers the movement of the sprocket wheel and the digging chain. A digging chain support frame actuator, operatively coupled to the digging chain support frame, raises and lowers the digging chain support frame relative to the upright boom structure and the trencher carriage. It is preferable to locate the upright boom structure and the digging chain support frame so that the path of the digging chain is close to the carriage when the digging chain is excavating a trench.
The trencher is operated by activating the chain drive motor and by also activating the digging chain support frame actuator to move the digging chain to penetrate a working surface. As the digging chain travels around the powered sprocket wheel and the idler pulley wheel, the carriage moves in a backward direction so that the digging chain follows the carriage as it excavates a trench. To dig a curved trench, the carriage is turned to follow a curved path. The upright orientation of the path of the digging chain facilitates the excavation of a curved trench. When following a curved path, the upright digging chain does not interfere with the walls of the trench by a degree that is sufficient to significantly impede its operation. The proximate location of the digging chain relative to the carriage also minimizes the degree by which the digging chain will swing against one of the walls of the trench if the trencher transitions from a straight path to a curved path. Accordingly, it is relatively easy to execute a smooth transition from excavating a straight trench to excavating a curved trench. If the operator gradually turns the carriage to a curved path, the digging chain will smoothly transition to following a curved path.
Preferably, an auger assembly is adjustably mounted to the digging chain support frame. Such an auger assembly includes transversely mounted augers that are powered by an auger sprocket wheel that engages the digging chain. As the digging chain is removing material from a trench, the rotating augers move excavated material away from the trench and the trencher. The location of the augers can be changed to correspond to a desired trench depth.
It is also preferable to mount a pair of earth moving blades on either side of the digging chain support frame. The earth moving blades are adjustably mounted on arms that can be interconnected to rotate in unison relative to the trencher carriage. The earth moving blades can be placed in various positions suitable for pushing material away from an excavated trench, pushing material into an excavated trench or when locked together to define a single blade, smoothing or scraping a working surface.